const_cast 与 static_cast [英] const_cast vs static_cast

问题描述

将 const 添加到非常量对象中，哪种方法是首选?const_cast 或 static_cast.在最近的一个问题中，有人提到他们更喜欢使用 static_cast，但我原以为 const_cast 会使代码的意图更加清晰.那么使用 static_cast 使变量为 const 的参数是什么?

To add const to a non-const object, which is the prefered method? const_cast<T> or static_cast<T>. In a recent question, someone mentioned that they prefer to use static_cast, but I would have thought that const_cast would make the intention of the code more clear. So what is the argument for using static_cast to make a variable const?

推荐答案

不要使用.初始化引用对象的常量引用:

Don't use either. Initialize a const reference that refers to the object:

T x;
const T& xref(x);

x.f();     // calls non-const overload
xref.f();  // calls const overload

或者，使用 implicit_cast 函数模板，例如 Boost 中提供的:

Or, use an implicit_cast function template, like the one provided in Boost:

T x;

x.f();                           // calls non-const overload
implicit_cast<const T&>(x).f();  // calls const overload

考虑到 static_cast 和 const_cast 之间的选择，static_cast 绝对是可取的:const_cast 应该只用于抛弃 constness 因为它是唯一可以这样做的演员，而抛弃 constness 本质上是危险的.通过丢弃常量获得的指针或引用修改对象可能会导致未定义的行为.

Given the choice between static_cast and const_cast, static_cast is definitely preferable: const_cast should only be used to cast away constness because it is the only cast that can do so, and casting away constness is inherently dangerous. Modifying an object via a pointer or reference obtained by casting away constness may result in undefined behavior.

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